The present invention is in general related to a zero voltage, zero current switching boost converter which utilizes electronic switches to accomplish voltage boost operation.
FIG. 1 illustrates a single-phase boost converter. In FIG. 1, when the main switch Sm turns on, the direct current (DC) power outputted from the full-wave rectifier will start to accumulate electric energy on the boost choke L. The main diode Dm is turned off at this moment. When the main switch Sm turns off, the current will drop off instantaneously and the current transition rate (di/dt) of the boost choke L becomes negative. An inverse electromotive force of a magnitude of L(di/dt) is induced across the boost choke L. Thereby the main capacitor will be charged to achieve the function of voltage boost. Theoretically, the main switch Sm will rapidly and periodically turn on and off so that the electric energy stored in the boost choke L is able to discharge to the main capacitor at any time. In this manner, the main capacitor can maintain a constant voltage.
However, the boost converter of FIG. 1 is disadvantageous over the situation that when the main switch Sm is switching its state, the main switch Sm and the main diode Dm will incur a serious switching loss due to a reverse recovery current introduced by the main diode Dm.
FIG. 2 is an improved boost converter which is designed for obviating the foregoing disadvantages encountered by the prior art boost converter of FIG. 1. The circuit configuration of FIG. 2 principally locates a branch circuit across the circuit nodes of the main switch Sm and also locates another branch circuit across the main diode Dm. The auxiliary inductor La and the auxiliary switch Sa on the branch circuit can be applied to eliminate the reverse recovery current of the main diode Dm and preload electric energy onto the auxiliary inductor La. Then the main switch Sm can be turned on under a zero voltage circumstances so that the energy stored in the auxiliary inductor La can be discharged through the diode D2 to the output capacitor when the auxiliary switch Sa is turned off. Therefore the deficiency of high switching loss arising from the main diode of the boost converter of FIG. 1 can be eliminated. However, in FIG. 2, the switching loss arising from the auxiliary switch Sa is still existed, and further the problems of electromagnetic interference (EMI) and radio frequency interference (RFI) still have not been addressed.
An object of the present invention is the provision of a boost converter which enables the electronic switches thereof to switch their on/off states under a zero voltage/zero current circumstances, to avoid switching loss and reduce electromagnetic interference and radio frequency interference. In addition, the switch element of the boost converter can be of a miniaturized size and the overall performance can be enhanced.
To achieve the foregoing objectives, a zero voltage, zero current switching boost converter is proposed and comprises a boost section for receiving a first direct current (DC) power and outputting a boosted second direct current power, a resonant circuit comprising a first discharge loop including a first auxiliary switch and a second discharge loop including a second auxiliary switch for permitting the first direct current power to discharge alternately through the first discharge loop and the second discharge loop to a load to generate the second direct current power, and wherein the main switch is turned on and off under a zero voltage circumstances and both the first auxiliary switch and the second auxiliary switch are turned on and off under a zero current circumstances.
According to the zero voltage, zero current switching boost converter as described hereinbefore, the boost section further comprises a boost choke, and the load comprises a first output capacitor and a second output capacitor.
The first discharge loop further comprises a resonant inductor, the second output capacitor and a second main diode. The second discharge loop further comprises a first main diode, the first output capacitor and the resonant inductor.
Remarkably, both the first auxiliary switch and the second auxiliary switch comprise a unidirectional switch. A preferable implementation for the unidirectional switch is an insulated gate bipolar transistor (IGBT) with a relatively low collector-emitter reverse-biased voltage with gate opened (VCEO). An alternative for implementing the unidirectional switch is a silicon controlled rectifier (SCR) or an insulated gate bipolar transistor (IGBT) with a relatively high collector-emitter reverse-biased voltage with gate opened (VCEO). If both the first auxiliary switch and the second auxiliary switch are implemented by an insulated gate bipolar transistor (IGBT) with a relatively low collector-emitter reverse-biased voltage with gate opened (VCEO), a first auxiliary diode and a second auxiliary diode are required to respectively connect with the first auxiliary switch and the second auxiliary switch.